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Fencer Vulns
medium 5.5

CVE-2021-3995 json

A logic error was found in the libmount library of util-linux in the function that allows an...

published 2022-08-23 4 y ago modified 2026-07-23 3 mo ago also EUVD-2021-27185 , JLSEC-2025-192

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 50%
public exploits
0
none known

Summary

A logic error was found in the libmount library of util-linux in the function that allows an unprivileged user to unmount a FUSE filesystem. This flaw allows an unprivileged local attacker to unmount FUSE filesystems that belong to certain other users who have a UID that is a prefix of the UID of the attacker in its string form. An attacker may use this flaw to cause a denial of service to applications that use the affected filesystems.

Patch / fix

  • julia Libmount_jll 2.39.3+0
  • julia Libuuid_jll 2.39.3+0
  • julia util_linux_jll 2.39.3+0
  • kernel util-linux 2.37.3
  • util-linux Debian 14, Debian 13, Debian 12 2.37.3-1

debian advisories DEBIAN-CVE-2021-3995

  • util-linux Ubuntu 20.04 LTS 2.34-0.1ubuntu9.3
  • util-linux Ubuntu 22.04 LTS 2.37.2-4ubuntu2

ubuntu advisories UBUNTU-CVE-2021-3995

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • shadow SLE Module for Basesystem 15 SP3, SLE Micro 5.2, SLE Micro 5.1 4.8.1-150300.4.3.8
  • util-linux SLE Module for Basesystem 15 SP3, SLE Micro 5.2, SLE Micro 5.1 2.36.2-150300.4.14.3
  • libeconf SLE Module for Transactional Server 15 SP3, SLE Module for Basesystem 15 SP3, SLE Micro 5.2 +1 more 0.4.4+git20220104.962774f-150300.3.6.2
  • util-linux-systemd SLE Module for Server Applications 15 SP3, SLE Module for Basesystem 15 SP3, SLE Micro 5.2 +1 more 2.36.2-150300.4.14.2

suse advisories SUSE-SU-2022:0727-2SUSE-SU-2022:0727-1

  • util-linux openSUSE Tumbleweed 2.37.3-1.1
  • shadow openSUSE Leap 15.3 4.8.1-150300.4.3.8
  • util-linux openSUSE Leap 15.3 2.36.2-150300.4.14.3
  • libeconf openSUSE Leap 15.3 0.4.4+git20220104.962774f-150300.3.6.2
  • python3-libmount openSUSE Leap 15.3 2.36.2-150300.4.14.2
  • util-linux-systemd openSUSE Leap 15.3 2.36.2-150300.4.14.2

opensuse advisories openSUSE-SU-2024:11784-1openSUSE-SU-2022:0727-1

  • util-linux Alpine 3.24, Alpine 3.23, Alpine 3.22 +10 more 2.37.3-r0

alpine advisories ALPINE-CVE-2021-3995

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3995 updated cvss 4.7

util-linux: Unauthorized unmount of FUSE filesystems belonging to users with similar uid

  • Red Hat Enterprise Linux 6 uuidd, libuuid, libblkid, util-linux-ng Red Hat Enterprise Linux 7 uuidd, libuuid, libblkid, libmount, util-linux Red Hat Enterprise Linux 8 uuidd, libuuid, libblkid, libfdisk, libmount, util-linux, +3 more Red Hat Enterprise Linux 9 uuidd, libuuid, libblkid, libfdisk, libmount, util-linux, +4 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.64% chance of exploitation in the next 30 days, higher than 50% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • openwall.com https://www.openwall.com/lists/oss-security/2022/01/24/2 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
julia Libmount_jll
<2.39.3+0
2.39.3+0
julia Libuuid_jll
<2.39.3+0
2.39.3+0
julia util_linux_jll
<2.39.3+0
2.39.3+0

Affected products

  • n/a util-linux

Classification

Weakness
  • CWE-552 Files or Directories Accessible to External Parties

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.